Method of fabricating sub-miniature semiconductor matrix apparatus



Dec. 1, 1964 R SAUNDERS METHOD OF FABRICATING SUB-MINIATURE SEMI-CONDUCTOR MATRIX APPARATUS Filed June 5, 1961 a m E INVENTOR.

RALPH SAUNDERS AGENT United States Patent O 3 153 927 PVETHQE) OF FABRCA TNG SIJ-E'EINEATEE SEBHCGNDUCTOR MATRHX APARATS Raph Sannders, Havertcwn, Pa., assignor to Cerpnration, Detroit, Mish., a Corporation of Michigan Filed 5, wl, Ser. Ne. &4,253 12 Clans. (Ci. 29-1555) It is a further object or" the invention to provide a method for joining printed wlring busses to electrical semi-conductor circuit Components saudwiched between high dielectric material.

It is an additional object of the invention to provide an improved method for assembling and electrically interconnecting an array of m nute etched or ultrasonically machined electrical components, such as diodes, to printed wiring on dielectric structures.

It is still another object of the invention to provide a method of bonding silicon diodes to obverse and reverse printe-,d wiring panels thus to form a silicon diode matrix.

In accordance With the foregoing objects and first briefly described, the invention comprises the method or" bonding a plurality of semi-conductor elements to an array of printed wiring busses thus to form an electrical storage or switching matrix.

Additional objects and advantages of the invention will appear in the following detailed specification when read in conjunction with the drawings forming a part hereof and in which:

FIG. l is a plan view of a printed wiring ass-cmbly;

FiG. 2 is a sectional view along the line 2-2 of FIG. l;

FIG. 3 is a side elevational View, partially in section, of a diode array or matrix;

F G. 4 is a top plan View of the diode array of FIG. 3 adhesively Secured to the printed wiring assembly of FIG. l;

FIG. 5 is a sectional View of a soldering jig used in the present invention;

FGS. 6 and 7 are sectional views showing Chemical baths employed in the present invention;

FK?. 8 is a plan View of a diode matrix according to the present invention; and,

PIG. 9 is a secticnal View along line 9-9 of PIG. 8 of a portion of the diode matrix of FIG. 8.

Briefiy described, the method comprises the steps of providing a pair of separate printed circuit assemblies and a substrate support upon which semi-conductor elements, such as diodes, are releasably adhesively secured in a desired matrix array, bonding as by soldering-the printed circuits of one of the printed circuit assemblies to one side of the diodes with the printed circuits in one direction, removing the substrate by dissolving the adhesive, and finally bonding-again as by soldering-the printed circuits on the other printed circuit assembly to the other side of the diodes with the printed circuits arranged at right angles to those on the other printed circuit assembly.

Now specifically, and with reference to the drawings, it is seen in FIG. 1 that a preferred printed circuit assembly comprses a suitable dielectric circuit panel or plate ti?, such for example as Coming Pyrex #7740," screened, or otherwise provided, with a predetermined conductive pattern of busses 12 terminating in pads 12'. When screened' an electrically conductive material such as Du ?ont Conductive Prit, #7753, Gold, Platinum Paste is used. The "screened plate lt& is then fired at a ternperature of approximately 650-800 C. for a time suificient to produce a strong bond between the glass and the electrically conductive layer on the order of approximately ten minutes.

The fired plate 1 is then provided with a relatively thin coating of copper 14- (FIG. 2) preferably electroplated thereon, and to which is added by suitable means a plating 15, for example, or" /40 solder varying as desired from approximately .1 to .O0l" tbick.

lt is understood, of course, that other substrate material might be used to advantage, such as, for example, by substituting for the Pyrex glass plate 10 a glass or glass epoxy material which may be laminated or clad with Copper material on both suriaces. A conductive circuit pattern may then be provided by any well known printed circuit process thua to produce solder-plated circuits similar in Construction to the Pyrex plate lil. Still further, the circuit plate substrate could, of course, be made of other material such as ordinary glass, Copper clad phenolic or other sirnilar dielcctric material. r

The bnsses 12 and pads iz' of the prepared circuit plate i@ are then coated in a known manner with a layer of soldering -rux 18 such for example as Kestefis after which the fiuxed surface is dried in ambient air or, ir" desired, it may be more quickly dried in forced hot air to permit the fiux to become slightly tacky and adhesive in consistency.

An assembly 2% which may be fabricated as by etchetc. or by ultrasonic machining techniques set forth in a copending application to Frederick Ohntrup, Serial No. li i-,956, entitled Fabricating Tool and Technique, filed concurrently erewith on June 5, 1961 and assigned to the same assignee as the presen invention, to include an array of diodes 22 (FlG. 3) having a conductive solderable coating ;ES on opposite sides thereof and releasably bonded to a supporting substrate or transfer plate 24 by a soluble adhesve 25. The coating 28 is or may be a sintered eiectroless nickel, and bonds thoroughly and completely to the silicon surface of the wafer. The transfer plate 2 3 preferabiy is of ?yrex and the cement or adhesive 26 of a type capable of withstanding ultrasonic machining and temperatures in excess of approximately 500 E. for brief ods Without charring. A suitable cement, for example, is Laieside 7OC, manufactured by Hugh Cartwright Co., Chicago, ill.

The exposed top surfaces of the coated diodes 22 are sprayed or brushed With a suitable ux 3%, for example, Duntorfs "inners i lux (acid) manufactured by I- W. Bunton, Providence, RI., and thereafter the assembly is blotted to remove the excess flux.

The assernbly 2@ carrying the prepared diodes 22 is then joined to the printed circuit assembly lil by bringing the diode array into surface contact with the adhesively taclzy surface of the printed wiring on circuit plate ii), as seen in FG. 4. The diode array is properly and accnrately registered with the conductor busses 12 on the plate 10. Thereater, slight pressure is applied to cause the two assemblies l and Zt? to stick together in exact registration thus to form the assembly 32, after which the adhcsive is allowed to dry.

The dried assembly 32 is then placed under pressure in a suitable soldering xture such as shown at 34 of generally U-shaped configuration. Fixture 34 includes parallel spaced apart legs 36 and 38 and a centrally disposed back-up member 4@ carrying a pressure pad 42 and pivoted at its end 44 to the base 45 thereof. A spring 33 biases the member toward the leg 38 which is formed of a suitable beat transfer material, such as metal.

With the assembly 32. so disposed, the spring 48 causes the member 42 to press the diodes against the printed V wiring member conditioning the latter for soldering. By means of a heating eiement 59 in contact with heat ;transfer leg 38, adjustable for a desired temperature level by'means, not shown, and energized over leads 52 from,

a source of current 54, heat is transferred through leg 38 causin the solder to melt sufciently to bond the diodes to their respective printed wiring busses.

The soldered assembly 32 is removed from the fixture r 34 and placed in a shallow tray 54 containing a suitable soivent 56 such as trichlorethylene, which may be heated, so as to dissolve the bonding adhesive 26 thus to separate -the substrate 24- rom the diodes 22 and also more adequately to clean the remaining fiuX from the circuit plate and the diodes. The assembly is thereafter placed in a detergent solution 53 preferably at boiling temperature *to remove any remaining traces of dirt or other foreign material. The assembly is then rinsed clean, in water and/or alcohol for example, after which t s dred.

In the manner set forth hereinbefore a second circuitgized so as to solder'the busses of the second circuit plate to the opposite ends ofthe'diodes thus to form the assembly aas shown in FIG. 8.' This mul-ti-layer assemly 69 is then given a final etching treatment in an etchant which is compatible with the solder thus to remove roughness, if any, such as might be due to the ultrasonic machining operation of the diodes. Thereafter it is washed and rinsed and dred. r

Finally, if desired, suitable lead wires 62, FG; 9, may' be attached as by solder 64 to the pads 12' of each 'of the busses on the circuit plates whereby interconnection thereof may be made to other associated circuitry or utilization device such fo: example, as bearn switching or indicating tubes; Or, the assernbly may be employed as a plug-in unit by virtue of appropriate design of the pads.

What is claimed is: g

1.-A method of orming a miniature semi-conductor matrix comprisng the steps of, providing a dielectric supporting structure with a pattern of conductve busses printed thereon, providing a dielectric supporting structure with a plurality of semi-conductors bonded thereon by means of a sohble adhesive permitting subsequent removal of said supporting structure therefrom, applying a viscous flux to said busses, applying a fiux to said *semi-conductors, registering said semi-conductors and said busses, soldering said semi-conductors to said busses while'so registered and thereafter, removing the dielectric supporting ,structure from said semi-conductors leaving the latter firmly bonded to said busses.

2. A method of forming a miniature semi-conductor comprsing the steps of, providing a glass epoxy suppoiting structure with a pattern of columns and rows of :conductive busses printed thereon, providing a di iectric glass epoxy supporting structure with a plurality of Vertically disposed rows and columns of semi-conductors bonded thereon by means of a soluble adhesive permitting subsequent removal of said supporting structure therefrom, applying a viscous flux to said busses, applying a flux to said semi-conductors, registering the rows and columns of' semi-conductors with the rows and colurnns of busses,

soldering said semi-conductors to said busses while so registered and, thereafter, removing the dielectric supporting structure from said semi-conductors leaving the' substrate, bonding -a water of silicon material on sm'd substrate by means of a soluble adhesive permittng subsequent removal of said substrate therefrom, forming said silicon material into a plurality of rows and columns of individual silicon diodes, providing a dielectric supporting structure with a pattern of conductive busses i printed thereon in parallel spaced apart relationship and including enlarged conductive areas at one end of each conductive buss, applying a viscous flux to, said busses, drying said fiux to a tacky adhesive consistency, applying a luX to the surface of said diodes, registering sai-:l diodes with respective busses in said rows and columns, soidering i the diodes to the busses when so registered and, removing the dielectric supporting structure from the diodes leaving the latter firmly bonded to said busses, cleaning said assembly to remove any traces of fluX therefrom.

4-. A method of forming a miniature semi-conductor matrix comprisng the steps of, providing a dielectric substrate, bonding a water of silicon material onto said substrate by means of a soluble adhesive permitting subsequent removal of said substrate therefrom, forming said SlllCOn material on said substrate into a plurality of rows and colurnns of individual silicon diodes, providing a dielectric ,supporting structure with a pattern of conductive busses printed thereon in parallel spacedapart relationship and including enlarged conductive areas at one end of each conductve buss, applying viscous fiuX to said busses, drying said'fiux to a tacky adhesive consistency, applying a fluX to the exposed surface of said diodes, registering said diodes with respective'busses in said rows and columns, soldering the diodes to the busses when so registered, removing the dielectric substrate from the i diodes leaving the latter firmly bonded to the busses with their opposite ends exposed, providing a second dielectric supporting structure with a pattern of conductive busses printed thereon in parallel spaced apart relationship, and including enlarged conductive areas at one end of each bus, registering the conductive pattern of busses of the second dielectric supporting structure 'at right angles to the original condutive busses with the individual diodes, bondirg the eXposed ends of the diodes to said second set of conductive-busses forming an orthogonal matrix and finally, cleaning said assembly to remove any traces of flux therefrom.

5. A method of forming a miniature semi-conductor matrix comprising the steps of, providing a dielectric substrate, bonding a water of silicon material on said substrate by means of a soluble adhesive permitting subsequent removal of said substrate therefrom, forming said silicon material into a plurality of rows and columns of individual diodes, providing a diele'ctric supporting structure with a pattern of conductive busses printed thereon in parallel spaced apart relationship and including enlarged conductive areas *at one end of each conductive busaapplying .a viscous fluxto said busses, drying said to a tacky adhesive consistency, applying a flux V to the surface of said diodes, register-ing said diodes I with respective busses in said rows and columns, solder- ,ing the diodes to the busses when so registered, and, removing the dielectr'c supporting structure from the diodes leaving the latter firmly bonded to said busses, cleaning said assembly to remove any traces of flux therefrom, applying electrical lead wire conductors to said busses.

6. The method of transferring electrical components' and pressure sufficient to cause said solder to bond said Component to said conductor, and finally dissolving said adhesive and removing the substrate element upon which said Component was supported leaving the Component securely bonded to the conductor.

7. A method of transferring diodes from a supporting structure to a printed wirng assembly comprising, securing a diode upon a supporting substrate element by means of a soluble adhesive, providing an exposed surface of said diode with a solderable coating and a tacky adhesive flux, securing an electrical conductor on a dielectric substrate, coating said conductor with a film of solder and a tacky adhesive flux, joining said substrates by bringing said diode into contact with said conductor whereby the tacky adhesive fiux secures them together, subjecting said joined substrates to heat and pressure sufiicient to cause said solder to bond said diode to said conductor, and finally dissolving said adhesive and removing the substrate element upon which said diode was supported leaving the diode securely bonded to the conductor.

8. The method of transferring electrical Components from a supporting structure to a printed wiring assembly comprising, securing a plurality of electrical components in rows upon a substrate element by means of a soluble adhesive, providing an exposed surface of each of said Components with a solderable coating, securing a plurality of electrical conductors in arallel on a dielectric substrate, coating said conductors with a film of solder, providing a tacky adhesive flux on the eXposed surfaces of said Components and the conductors, joining said su strates by bringing respective of said rows of Components into contact with a conductor whereby the tacky adhesive fluX secures them together, subjecting said joined substrates to heat and pressure suicient to cause said solder to bond said Components to said conductors, and finally dissolving said adhesive and removing the substrate element upon which said Components were supported, leaving the Components securely bonded to said conductors.

9. The method of transferring diodes from a supporting structure to a printed wirng assembly comprising, securing a plurality of diodes in rows upon a supporting substrate element by means of a soluble adhesive, providing an exposed surface of each of said diodes with a solderable coating and a tacky adhesive flux, securing a plurality of electrical conductors in parallel on a dielectric substrate, coating said conductors with a film of solder and a tacky adhesive fiux, joining said substrates by bringing respective of said rows of diodes into contact with a conductor whereby the tacky adhesive flux secures them together, subjecting said joined substrates to heat and pressure sufiicient to cause said solder to bond said diodes to said conductors, and finally dissolving said adhesive and removing the substrate element upon which said diodes were supported, leaving the diodes securely bonded to said conductors.

10. The method of fabicating subminiature component matrix apparatus comprising the steps of, securing an array of Components in rows and columns on a substrate element by means of a soluble adhesive, opposite surfaces of said Components being provided with a solderable coating, providing first and second printed wiring assemblies each including a plurality of substantially parallel electrical conductors printed on a dielectric substrate element, applying a tacky adhesive flux to the exposed surfaces of said conductors and said Components, joining the first of said printed circut assemblies with said component substrate element by bringing said components into contact with the conductors on said first printed circut assembly whereby the tacky adhesive flux secures them together with said conductors crossng the rows of components, subjecting said joined substrates to heat and pressure sutlicient to cause said solder to bond said components to said printed conductors, dissolving said adhesive and removing the substrate element upon which the Components were supported, applying a tacky adhesive x to the now eXposed surfaces of said components, joining said second printed circut assembly with the now exposed surfaces of said semi-conductor components by bringing them into contact whereby the tacky adhesive fiux secures them together with the conductors on said second printed circut assembly traversing the columns of said components at right angles to the conductors on the first printed circut assembly, and subjecting the now joined substrates again to heat and pressure sufiicient to cause said solder to bond said Components with the conductors on said second printed circut assembly.

11. The method of fabricating subminiature diode ma*- riX apparatus comprisng the steps of, securing an array of diodes in rows and columns on a substrate element by means of a soluble adhesive, opposite surfaces of said diodes being provided with a solderable coating, providing first and second printed wiring assemblies each inciuding a plurality of substantially parallel electrical conductors printed on a dielectric substrate eiement, applying a tacky adhesive fluX to the eXposed surfaces of said conductors and said diodes, joim'ng the first of said printed circut assemblies with said diode substrate element by bringing said diodes into contact with the conductors on said first printed circut assembly whereby the tacky adhesive flux secures them together with said conductors crossng the rows of diodes, subjecting said joined substrates to heat and pressure sucient to cause said solder to bond said diodes to said printed conductors, dissolving said adhesive and removing the substrate element upon which the diodes were supported, cleaning the remaining flux from the first printed ci'cuit assembly now including the diodes, providing the now exposed surfaces of said diodes with a tacky adhesive ux, joining said second printed circut assembly with the now exposed surfaces of said diodes by bringing them into contact whereby the tacky adhesive fiux secures them together with the conductors on said second printed circut assembly traversing the columns of diodes at right angles to the conductors on the first printed circut assembly, subjecting said now joined substrates again to heat and pressure suflicient to cause said solder to bond said diodes with the conductors on said second printed circut assembly, and finally washing the resultant product to remove eXcess ux therefrom.

12. The method of fabricating subminiature diode matrX apparatus comprising the steps of, forming an array of diodes in rows and columns on a substrate element by ultrasonic machining of a film of semi-conductors laid on said element, said semi-conductors being afixed to said substrate element by means of soluble adhesive permitting said substrate subsequently to be removed therefrom, opposite surfaces of said diodes being provided with a solderable coating, providing first and second printed wiring assemblies each including a plurality of substantially parallel electrical conductors printed on a dielectric substrate element, applying a tacky adhesive soldering fiux to the eXposed surfaces of said conductors and said diodes, joining the first of said printed circut assemblies with said array of diodes by bringing said diodes into contact with the conductors on said first printed circut assembly whereby the tacky adhesive flux secares them together With said conductors crossng the rows of diodes, subjecting said substrates to heat and pressure sufiicent to cause said solder to melt and bond said diodes to said printed conductors, dissolvirg said adhesive in a heated solvent bath and removing the substrate element upon which the diodes were supported, cleaning the remaining flux from the first printed circut assembly now including the diodes, providing the now exposed surfaces of said diodes with a tacky adhesive soldering flux, joinng said second printed circut assembly with the now exposed surfaces of said diodes by bringing them into contact whereby the tacky adhesive fluX secures them together with the conductors on said second printed circut assembly traversing the columns of diodes at right angles 'said dodes with the conductors on said second prnted circuit assembly, and finally Washng the resultant product in a cleansing solution to remove excess flux therefrom.

References cited in the file of this patent UNITED STATES PATENTS 1,963,834 Decker June 19, 1934 2,714,143 Howatt July 26, 1955 2,850,681 Hoflon Sept. 2, 1958 &158327 I.B.M; Technical Dsclosure Bulletin, vol. 1, No. 5,?

Schaper Jan. 13, 1959 Leno Sept. 1, 1959 Daves et al. May 24, 1960 Lathrop June 20, 1961 Shockley Aug. 1, 1961 FOREIGN PATENTS France j May 30, 1960 OTHER REFERENCES February 1959, Transstor Mouhtng, E. Barrows, 

1. A METHOD OF FORMING A MINIATURE SEMI-CONDUCTOR MATRIX COMPRISING THE STEPS OF, PROVIDING A DIELECTRIC SUPPORTING STRUCTURE WITH A PATTERN OF CONDUCTIVE BUSSES PRINTED THEREON, PROVIDING A DIELECTRIC SUPPORTING STRUCTURE WITH A PLURALITY OF SEMI-CONDUCTORS BONDED THEREON BY MEANS OF A SOLUBLE ADHESIVE PERMITTING SUBSEQUENT REMOVAL OF SAID SUPPORTING STRUCTURE THEREFROM, APPLYING A VISCOUS FLUX TO SAID BUSSES, APPLYING A FLUX TO SAID SEMI-CONDUCTORS, REGISTERING SAID SEMI-CONDUCTORS AND SAID BUSSES, SOLDERING SAID SEMI-CONDUCTORS TO SAID BUSSES WHILE SO REGISTERED AND THEREAFTER, REMOVING THE DIELECTRIC SUPPORTING STRUCTURE FROM SAID-CONDUCTORS LEAVING THE LATTER FIRMLY BONDED TO SAID BUSSES. 